One of the country’s most notorious murderers, Knysna DJ Heinrich van Rooyen, has allegedly been running a business, operating a YouTube channel and updating his LinkedIn page — all from inside his prison cell.

Van Rooyen, imprisoned for life after he killed two waitresses almost two decades ago, was allegedly helping to run the family construction business from a cellphone which was found in his cell at the Medium B section of the St Albans prison...